Electromagnetic wave absorbers for preventing the leak and intrusion of electromagnetic waves are used in electronic and communications apparatuses and systems such as personal computers, cell phones, automatic toll-collecting systems (ETC) on toll roads, wireless LAN, etc. Electromagnetic wave absorbers are required to efficiently absorb electromagnetic waves in a wide frequency range, with little difference in electromagnetic wave absorbability depending on incident directions (anisotropy of electromagnetic wave absorbability). Further, in systems using circularly polarized electromagnetic waves such as ETC, etc., electromagnetic wave absorbers are required to efficiently absorb both of TE waves (electromagnetic waves whose electric field components are perpendicular to an incident surface) and TM waves (electromagnetic waves whose magnetic field components are perpendicular to an incident surface).
Though electromagnetic wave absorbers formed by metal sheets or nets are widely used at present, electromagnetic wave-absorbing sheets having vapor-deposited metal layers formed on plastic sheets were recently proposed. For instance, JP 9-148782 A proposes an electromagnetic wave-absorbing sheet comprising a plastic film, and first and second vapor-deposited aluminum layers formed on both surfaces thereof, the first vapor-deposited aluminum layer being etched to a non-conductive linear pattern, and the second vapor-deposited aluminum layer being etched to a network conductive pattern. However, this electromagnetic wave-absorbing sheet has a periodic linear pattern and a periodic network pattern, it cannot efficiently absorb electromagnetic waves in a wide frequency range, and its electromagnetic wave absorbability has large anisotropy.
JP 11-40980 A proposes a electromagnetic wave shield having a vapor-deposited copper layer and a vapor-deposited nickel layer formed in this order on one surface of a plastic film. However, this electromagnetic wave shield has insufficient electromagnetic wave absorbability with large anisotropy.